Method for reducing low speed pre-ignition

ABSTRACT

Use of a gasoline fuel composition for reducing the occurrence of Low Speed Pre-Ignition (LSPI) in a spark-ignition internal combustion engine, wherein the gasoline fuel composition comprises a gasoline base fuel and has a PM Index of 1.4 or less.

FIELD OF THE INVENTION

The present invention relates to a method for reducing low speedpre-ignition in a spark-ignition internal combustion engine.

BACKGROUND OF THE INVENTION

Under ideal conditions, normal combustion in a conventionalspark-ignited engine occurs when a mixture of fuel and air is ignitedwithin the combustion chamber inside the cylinder by the production of aspark originating from a spark plug. Such normal combustion is generallycharacterized by the expansion of the flame front across the combustionchamber in an orderly and controlled manner.

However, in some instances, the fuel/air mixture may ignite prematurelyprior to the spark plug firing, or after it fires and the ensuing flamefront compressing and heating unburned end gases, thereby resulting in aphenomenon known as pre-ignition. Pre-ignition is undesirable as ittypically results in the presence of greatly increased temperatures andpressures within the combustion chamber, which may have a significant,negative impact on the overall efficiency and performance of an engine.Pre-ignition may lead to “mega-knock” events which can cause damage tothe cylinders, pistons and valves in the engine and in some instancesmay even culminate in engine failure.

Recently, low-speed pre-ignition (“LSPI”) has been recognized amongstmany original equipment manufacturers (“OEMs”) as a potential problemfor highly boosted, down-sized spark-ignition engines, in particularhigh compression ratio direct injection spark-ignition engines. Contraryto the pre-ignition phenomenon observed in the late 50's at high speeds,LSPI typically occurs at low speeds and high loads. LSPI is a constraintthat restricts improvements in torque at low engine speeds, which couldimpact fuel economy and drivability. The occurrence of LSPI mayultimately lead to so-called “monster knock” or “mega-knock” wherepotentially devastating pressure waves can result in severe damage tothe piston and/or cylinder. As such, any technology that can mitigatethe risk of pre-ignition, including LSPI, would be highly desirable.

There are multiple mechanisms leading to LSPI events discussed in theliterature. One of those mechanisms involves ignition of the flaked-offdeposits present inside the combustion chamber (e.g. around the pistoncrevice region or on the injector and cooler regions behind the sparkplug) leading to LSPI events while another mechanism is based on theignition of oil droplets inside the combustion chamber. It could be acombination of these two mechanisms (deposits and oil droplets) thatresults in LSPI or a yet to be determined mechanism.

It has been found that LSPI is more common in engines, such as moderndownsized turbocharged spark ignition engines, that operate using anengine oil with high calcium content and a market-average gasoline fuel.Most commercial engine oils currently available in the market have highcalcium content, generally ranging from 1200 ppm to 3000 ppm. Typically,as mentioned above, this LSPI phenomenon is common in the high torque,low speed operating conditions. Most Original Equipment Manufacturers(OEMs) calibrate their engine management systems to restrict engineoperation in these regimes to prevent LSPI from occurring. However,operating in these regimes would potentially give the OEMs additionalopportunity to decrease fuel consumption.

One solution to the problem of LSPI is to formulate engine oils suchthat they have a new composition. Examples of those methods can be foundin WO2015/171978A1, WO2016/087379A1, WO2015/042341A1. One such solutionis to formulate engine oils having a very low calcium content (<500ppm). The effects of lower calcium content in the engine oils inreducing LSPI occurrences have been described in SAE 2016-01-2275. Sucha formulation potentially modifies the chemical pathways in terms of theoil droplets that lead to LSPI. However, most current commercial engineoils have medium to high calcium content and therefore it would bedesirable to come up with an alternative solution for the problem ofLSPI without having to reformulate the engine oil formulation.

U.S. Ser. No. 62/573,723 relates to a method for reducing low speedpre-ignition by using a gasoline formulation which comprises a certaintype of detergent additive package and/or certain detergent additivecomponents, especially in the case when used in engines which arelubricated with engine oils having high levels of calcium.

SAE International Paper SAE-2010-01-2115 published 25 Oct. 2010 relatesto an investigation of the relationship between gasoline properties andvehicle particulate matter emissions. In the investigation describedtherein, various chemical species were individually blended with anindolene base fuel and the solid particulate number (PN) emissions fromeach blend were measured over the New European Driving Cycle (NEDC). Apredictive model, termed the ‘PM Index’, was constructed based on theweight fraction, vapour pressure and double bond equivalent (DBE) valueof each component in the fuel. It was confirmed that the PM Index couldaccurately predict not only the total PN trend but also totalparticulate matter (PM) mass, regardless of engine type or test cycle.

It has now been found by the present inventors that by using a gasolineformulation which has a certain maximum Particulate Matter (PM) Index(as calculated according to the PM Index equation set out in SAEInternational Paper 2010-01-2115), a surprising reduction in LSPI eventscan be achieved, especially in the case when used in engines which arelubricated with engine oils having high levels of calcium.

SUMMARY OF THE INVENTION

According to the present invention there is provided the use of agasoline fuel composition for reducing the occurrence of Low SpeedPre-Ignition (LSPI) in a spark-ignition internal combustion engine,wherein the gasoline fuel composition has a PM Index of 1.4 or less.

According to the present invention there is further provided a methodfor reducing the occurrence of Low Speed Pre-Ignition (LSPI) in aspark-ignition internal combustion engine, the method comprisingsupplying to the engine a gasoline fuel composition having a PM Index of1.4 or less.

The features and advantages of the present invention will be apparent tothose skilled in the art. While numerous changes may be made by thoseskilled in the art, such changes are within the spirit of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate certain aspects of some of the embodiments ofthe invention, and should not be used to limit or define the invention.

FIG. 1 illustrates the test procedure which was used for engine tests inthe Examples hereinbelow.

FIG. 2 is a plot of the results in Table 6 below.

FIG. 3 is a plot of the results in Table 7 below.

DETAILED DESCRIPTION OF THE INVENTION

Fuel compositions for use herein generally comprise a gasoline base fueland optionally one or more fuel additives. Fuel compositions comprisinga gasoline base fuel are therefore gasoline fuel compositions. Thegasoline fuel compositions herein have a maximum PM Index.

The PM Index of a gasoline fuel composition can be calculated hereinusing Equation (1) below (as disclosed in SAE-2010-01-2115):

$\begin{matrix}{{{PM}{Index}} = {{\sum\limits_{i = 1}^{n}I_{\lbrack{443K}\rbrack}} = {\sum\limits_{i = 1}^{n}\left( {\frac{{DBE_{i}} + 1}{V.{P\left( {443K} \right)}_{i}} \times Wt_{i}} \right)}}} & {{Equation}(1)}\end{matrix}$

In Equation (1), a number, or i, is assigned to each gasoline componentin the gasoline composition, DBE_(i) is the double bond equivalent valueof component i, V.P(443K)_(i) is the vapour pressure of component i at443K, and Wt_(i) is weight fraction of component i in the gasolinecomposition.

Further details of the origin of this equation for calculating the PMIndex can be found in SAE paper SAE-2010-01-2115, incorporated herein byreference in its entirety.

The gasoline fuel compositions for use in the present invention have aPM Index of 1.4 or less, preferably 1.3 or less, more preferably 1.2 orless, even more preferably 1.1 or less, especially 1.0 or less. In apreferred embodiment herein, the fuel compositions have a PM Index of0.9 or less, preferably 0.8 or less, more preferably 0.7 or less, evenmore preferably 0.6 or less, especially 0.5 or less.

In one embodiment herein, the fuel compositions have a PM Index in therange of 0.4 to 1.4.

The level of occurrence of pre-ignition in a spark-ignited engine may beassessed using any suitable method. Such a method may involve running aspark-ignited engine using the relevant fuel and/or lubricantcomposition, and monitoring changes in engine pressure during itscombustion cycles, i.e., changes in pressure versus crank angle. Apre-ignition event will result in an increase in engine pressure beforesparking, or even after sparking where the flame front progressingacross the cylinder excessively compresses and heats the unburned endgases to the point of spontaneous ignition: this may occur during someengine cycles but not others. Instead, or in addition to, crank anglelocation may be monitored, for example at an early burn cycle initiationbefore spark, or at the start of combustion (SOC). Instead, or inaddition to, changes in engine performance may be monitored, for exampleby maximum attainable brake torque, engine speed, intake pressure and/orexhaust gas temperature. Instead, or in addition to, a suitablyexperienced driver may test-drive a vehicle which is driven by thespark-ignited engine, to assess the effects of a particular fuel and/orlubricant composition on, for example, the degree of engine knock orother aspects of engine performance. Instead, or in addition to, levelsof engine damage due to pre-ignition, for example due to the associatedengine knock, may be monitored over a period of time during which thespark-ignited engine is running using the relevant fuel and/or lubricantcomposition.

A reduction in the occurrence of pre-ignition may be a reduction in thenumber of engine cycles at which pre-ignition events occur or areduction in the rate at which pre-ignition events occur within theengine, and/or in the severity of the pre-ignition events which occur(for example, the degree of pressure change which they cause). It may bemanifested by a reduction in one or more of the effects whichpre-ignition can have on engine performance, for example impairment ofbrake torque or inhibition of engine speed. It may be manifested by areduction in the amount or severity of engine knock, in particular by areduction in, or elimination of, “mega knock”. Preferably, in thepresent invention, a reduction in the occurrence of pre-ignition is areduction in the number of engine cycles in which pre-ignition eventsoccur.

Since pre-ignition, particularly if it occurs frequently and leads to“mega-knock”, can cause significant engine damage, the fuel compositionsdisclosed herein may also be used for the purpose of reducing enginedamage and/or for the purpose of increasing engine longevity.

The uses and methods of the present invention may be used to achieve anydegree of reduction in the occurrence of pre-ignition in the engine,including reduction to zero (i.e., eliminating pre-ignition). It may beused to achieve any degree of reduction in a side effect ofpre-ignition, for example engine damage. It may be used for the purposeof achieving a desired target level of occurrence or side effect. Themethod and use herein preferably achieves a 5% reduction or more in theoccurrence of pre-ignition in the engine, more preferably a 10%reduction or more in the occurrence of pre-ignition in the engine, evenmore preferably a 15% reduction or more in the occurrence ofpre-ignition in the engine, and especially a 30% reduction or more inthe occurrence of pre-ignition in the engine. In an especially preferredembodiment, the method and use herein achieves a 50% reduction or morein the occurrence of pre-ignition in the engine. In another especiallypreferred embodiment, the method and use herein completely removes theoccurrence of pre-ignition in the engine.

Examples of suitable methods for measuring Low Speed Pre-Ignition eventscan be found in the following SAE papers: SAE 2014-01-1226, SAE2011-01-0340, SAE 2011-01-0339 and SAE 2011-01-0342. Another example ofa suitable method for measuring Low Speed Pre-Ignition events is thetest method described in the Examples hereinbelow.

The gasoline fuel compositions herein comprise a gasoline base fuel. Thegasoline base fuel may be any gasoline base fuel suitable for use in aninternal combustion engine of the spark-ignition (gasoline) type knownin the art, including automotive engines as well as in other types ofengine such as, for example, off road and aviation engines. The gasolineused as the base fuel in the liquid fuel composition of the presentinvention may conveniently also be referred to as ‘base gasoline’.

Gasolines typically comprise mixtures of hydrocarbons boiling in therange from 25 to 230° C. (EN-ISO 3405), the optimal ranges anddistillation curves typically varying according to climate and season ofthe year. The hydrocarbons in a gasoline may be derived by any meansknown in the art, conveniently the hydrocarbons may be derived in anyknown manner from straight-run gasoline, synthetically-produced aromatichydrocarbon mixtures, thermally or catalytically cracked hydrocarbons,hydro-cracked, hydro-isomerized petroleum fractions, catalyticallyreformed hydrocarbons or mixtures of these. Sulfur and nitrogen levelsin the final gasoline should be minimized by, for example, judicioushydro-treating to within the regulated specifications for the respectiveregional market. All of these gasoline components may be derived fromfossil carbon or renewables.

The specific distillation curve, hydrocarbon composition, researchoctane number (RON) and motor octane number (MON) of the gasoline arenot critical for the present invention.

Conveniently, the research octane number (RON) of the gasoline may be atleast 80, for instance in the range of from 80 to 110, preferably theRON of the gasoline will be at least 90, for instance in the range offrom 90 to 110, more preferably the RON of the gasoline will be at least91, for instance in the range of from 91 to 105, even more preferablythe RON of the gasoline will be at least 92, for instance in the rangeof from 92 to 103, even more preferably the RON of the gasoline will beat least 93, for instance in the range of from 93 to 102, and mostpreferably the RON of the gasoline will be at least 94, for instance inthe range of from 94 to 100 (EN 25164); the motor octane number (MON) ofthe gasoline may conveniently be at least 70, for instance in the rangeof from 70 to 110, preferably the MON of the gasoline will be at least75, for instance in the range of from 75 to 105, more preferably the MONof the gasoline will be at least 80, for instance in the range of from80 to 100, most preferably the MON of the gasoline will be at least 82,for instance in the range of from 82 to 95 (EN 25163).

Typically, gasolines comprise components selected from one or more ofthe following groups; saturated hydrocarbons, olefinic hydrocarbons,aromatic hydrocarbons, and oxygenated hydrocarbons. Conveniently, thegasoline may comprise a mixture of saturated hydrocarbons, olefinichydrocarbons, aromatic hydrocarbons, and, optionally, oxygenatedhydrocarbons.

Typically, the olefinic hydrocarbon content of the gasoline is in therange of from 0 to 40 percent by volume based on the gasoline (ASTMD1319); preferably, the olefinic hydrocarbon content of the gasoline isin the range of from 0 to 30 percent by volume based on the gasoline,more preferably, the olefinic hydrocarbon content of the gasoline is inthe range of from 0 to 20 percent by volume based on the gasoline.

Typically, the aromatic hydrocarbon content of the gasoline is in therange of from 0 to 70 percent by volume based on the gasoline (ASTMD1319), for instance the aromatic hydrocarbon content of the gasoline isin the range of from 10 to 60 percent by volume based on the gasoline;preferably, the aromatic hydrocarbon content of the gasoline is in therange of from 0 to 50 percent by volume based on the gasoline, forinstance the aromatic hydrocarbon content of the gasoline is in therange of from 10 to 50 percent by volume based on the gasoline.

The benzene content of the gasoline is at most 2 percent by volume, morepreferably at most 1 percent by volume based on the gasoline.

The gasoline preferably has a low or ultra low sulphur content, forinstance at most 1000 ppmw (parts per million by weight), preferably nomore than 500 ppmw, more preferably no more than 100, even morepreferably no more than 50 and most preferably no more than even 10ppmw.

The gasoline also preferably has a low total lead content, such as atmost 0.005 g/l, most preferably being lead free—having no lead compoundsadded thereto (i.e. unleaded).

When the gasoline comprises oxygenated hydrocarbons, at least a portionof non-oxygenated hydrocarbons will be substituted for oxygenatedhydrocarbons. The oxygen content of the gasoline may be up to 35 percentby weight (EN 1601) (e.g. ethanol per se (i.e. pure anhydrous ethanol))based on the gasoline. For example, the oxygen content of the gasolinemay be up to 25 percent by weight, preferably up to 10 percent byweight. Conveniently, the oxygenate concentration will have a minimumconcentration selected from any one of 0 and 5 percent by weight, and amaximum concentration selected from any one of 30, 20, 10 percent byweight. Preferably, the oxygenate concentration herein is 5 to 15percent by weight.

Examples of oxygenated hydrocarbons that may be incorporated into thegasoline include alcohols, ethers, esters, ketones, aldehydes,carboxylic acids and their derivatives, and oxygen containingheterocyclic compounds. All of the above oxygenates may containsaturated and/or unsaturated hydrocarbon backbones, as well as aromaticmoieties. Preferably, the oxygenated hydrocarbons that may beincorporated into the gasoline are selected from alcohols (such asmethanol, ethanol, propanol, 2-propanol, butanol, tert-butanol,iso-butanol, prenol, isoprenol and 2-butanol), ethers (preferably etherscontaining 5 or more carbon atoms per molecule, e.g., methyl tert-butylether and ethyl tert-butyl ether) and esters (preferably esterscontaining 5 or more carbon atoms per molecule); a particularlypreferred oxygenated hydrocarbon is ethanol.

When oxygenated hydrocarbons are present in the gasoline, the amount ofoxygenated hydrocarbons in the gasoline may vary over a wide range. Forexample, gasolines comprising a major proportion of oxygenatedhydrocarbons are currently commercially available in countries such asBrazil and U.S.A., e.g. ethanol per se and E85, as well as gasolinescomprising a minor proportion of oxygenated hydrocarbons, e.g. E10 andE5. Therefore, the gasoline may contain up to 100 percent by volumeoxygenated hydrocarbons. E100 fuels as used in Brazil are also includedherein. Preferably, the amount of oxygenated hydrocarbons present in thegasoline is selected from one of the following amounts: up to 85 percentby volume; up to 70 percent by volume; up to 65 percent by volume; up to30 percent by volume; up to 20 percent by volume; up to 15 percent byvolume; and, up to 10 percent by volume, depending upon the desiredfinal formulation of the gasoline. Conveniently, the gasoline maycontain at least 0.5, 1.0 or 2.0 percent by volume oxygenatedhydrocarbons.

Examples of suitable gasolines include gasolines which have an olefinichydrocarbon content of from 0 to 20 percent by volume (ASTM D1319), anoxygen content of from 0 to 5 percent by weight (EN 1601), an aromatichydrocarbon content of from 0 to 50 percent by volume (ASTM D1319) and abenzene content of at most 1 percent by volume.

Also suitable for use herein are gasoline blending components which canbe derived from a biological source. Examples of such gasoline blendingcomponents can be found in WO2009/077606, WO2010/028206, WO2010/000761,European patent application nos. 09160983.4, 09176879.6, 09180904.6, andU.S. patent application Ser. No. 61/312,307.

Whilst not critical to the present invention, the base gasoline or thegasoline composition of the present invention may conveniently includeone or more optional fuel additives. The concentration and nature of theoptional fuel additive(s) that may be included in the base gasoline orthe gasoline composition used in the present invention is not critical.Non-limiting examples of suitable types of fuel additives that can beincluded in the base gasoline or the gasoline composition used in thepresent invention include anti-oxidants, corrosion inhibitors, antiwearadditives or surface modifiers, flame speed additives, detergents,dehazers, antiknock additives, metal deactivators, valve-seat recessionprotectant compounds, dyes, solvents, carrier fluids, diluents andmarkers. Examples of suitable such additives are described generally inU.S. Pat. No. 5,855,629. Suitable detergent/dispersants to minimizeengine and fuel delivery system deposits can be selected fromderivatives of PIB-Amines, Mannichs, Polyether Amines, Succinimides, andmixtures thereof.

Conveniently, the fuel additives can be blended with one or moresolvents to form an additive concentrate, the additive concentrate canthen be admixed with the base gasoline or the gasoline composition ofthe present invention.

The (active matter) concentration of any optional additives present inthe base gasoline or the gasoline composition of the present inventionis preferably up to 1 percent by weight, more preferably in the rangefrom 5 to 2000 ppmw, advantageously in the range of from 300 to 1500ppmw, such as from 300 to 1000 ppmw.

The fuel compositions may be conveniently prepared using conventionalformulation techniques by admixing one or more base fuels with one ormore performance additive packages and/or one or more additivecomponents.

Lubricant compositions for use in the spark ignition engines describedherein generally comprise a base oil and one or more performanceadditives, and should be suitable for use in a spark-ignited internalcombustion engine. In some embodiments, the lubricant compositionsdescribed herein may be particularly useful in a turbochargedspark-ignited engine, more particularly a turbocharged spark-ignitedengine which operates, or may operate, or is intended to operate, withan inlet pressure of at least 1 bar.

High calcium content in the oil is frequently found to exacerbate LowSpeed Pre-Ignition, and hence the present invention has been found to beparticularly useful in high calcium engine oil environments, but thepresent invention will be useful in any circumstances in which theengine is prone to Low Speed Pre-Ignition, regardless of oil calciumcontent. Hence, the lubricant compositions for use herein can have acalcium content of 0 ppmw or greater, preferably 500 ppmw or greater,more preferably 1000 ppmw or greater, even more preferably 1200 ppmw orgreater, yet more preferably 1500 ppmw or greater, especially 2000 ppmwor greater, as measured according to ASTM D5185.

In one embodiment of the invention, the lubricating compositioncomprises from 1200 ppmw to 3000 ppmw, on the basis of the totallubricating composition. In another embodiment herein, the lubricantcompositions have a calcium content from 1500 ppmw to 2800 ppmw,preferably from 2000 ppmw to 2800 ppmw, more preferably from 2500 ppmwto 2800 ppmw, on the basis of the total lubricating composition, asmeasured according to ASTM D5185.

Optional lubricant additives which may be included in the lubricatingcomposition herein include anti-wear agents, anti-foam agents,detergents, dispersants, corrosion inhibitors, anti-rust additives,anti-oxidants, extreme pressure additives, friction modifiers, viscosityindex improvers, pour point depressants, and the like.

The lubricant composition herein preferably has a magnesium content offrom 1 to 1000 ppmw, preferably from 200 to 800 ppmw, based on the totallubricant composition.

A preferred additive for use in the lubricant composition herein is azinc-based anti-wear additive, such as a zinc dithiophosphate compound.Zinc-based anti-wear additives are well known in the art of lubricatingcompositions. It is preferred that the level of zinc present in thelubricant composition is in the range of 0 to 1200 ppmw, preferably inthe range from 600 to 1200 ppmw, based on the total lubricantcomposition.

Another preferred lubricant additive for use herein is amolybdenum-based friction-reducing additive, such as molybdenumdithiocarbamate. Molybdenum-based friction-reducing additives are wellknown in the art of lubricating compositions. It is preferred that thelevel of molybdenum present in the lubricant composition herein is inthe range of 0 to 1000 ppmw, preferably in the range from 0 to 900 ppmw,more preferably from 0 to 500 ppmw, based on the total lubricantcomposition.

To facilitate a better understanding of the present invention, thefollowing examples of certain aspects of some embodiments are given. Inno way should the following examples be read to limit, or define, theentire scope of the invention.

Examples

Three different fuels were used in the present examples (Fuel A, Fuel Band Fuel C). The chemical compositions and the properties of these fuelsare shown in Table 1 below. All fuels were blended to have the same RON,MON and ethanol content, and Fuel B and C were blended to have the samearomatic content. The PM Index of each of the fuels was calculatedaccording to Equation (1) above (as published in SAE 2010-01-2115published 25 Oct. 2010).

TABLE 1 Fuel A Fuel B Fuel C T90, ° C. 123.20 149.50 185.20 FBP, ° C.170.20 194.00 208.70 Density, kg/m³ 730.90 758.40 759.10 RON 97.60 97.7097.60 MON 87.10 87.10 87.10 EtOH, vol % 10.7 10.2 10.2 Aromatics, vol. %9.8 31.1 31.1 Aromatics, C8 vol. % 8.0 24.1 6.1 Aromatics, C9/9+ vol. %1.2 6.4 24.1 n-Paraffins, vol. % 1.1 5.6 8.0 i-Paraffins, vol. % 52.141.9 40.0 Naphthenes, vol. % 20.3 5.8 5.5 Olefins, vol. % 4.9 4.4 4.7ASVP, kPa 61.10 50.40 73.10 DVPE, kPa 55.20 44.90 66.80 PM Index 0.491.36 2.83

The lubricant type used in the present Examples was a GF-5 certifiedhigh calcium containing lubricant of 5W-30 viscosity grade having acalcium content of 2763 ppm as measured according to ASTM D5185. Table 2below sets out the chemical and physical properties of the lubricant.

TABLE 2 Oil grade SAE 5W-30 Viscosity Modifier Comb Friction ModifierMoDTC Ca, ppm 2763 Mg, ppm 8 Mo, ppm 88 P, ppm 848 S, ppm 2369 Zn, ppm1021 HTHS 150° C. 3.12 Vk100 (cSt) 10.39 Vk40 (cSt) 60.11 ViscosityIndex 163

Fuels A, B and C were subjected to the following test method formeasuring LSPI events and the frequency thereof.

Test Method for Measuring LSPI

The test protocol used for measuring LSPI events in the present examplesis described below. The engine used was the GEM-T4 engine.

The commonly used variables for LSPI detection are:

(1) Crank angle location at an early burn cycle initiation before spark,i.e. 2% Mass Fraction Burned (MFB).

(2) the peak pressure during pre-ignition and combustion (at or beyond100 MPa or greater than the sum of mean peak pressure and 4.7 times thestandard peak pressure.

(3) Crank angle locations at the start of combustion (SOC) throughpost-processing software from FEV which uses an LSPI detection algorithm(further details of which can be found in Haenel et al, SAE Int. J.Fuels Lubr., Volume 10, Issue 1 (April 2017) entitled ‘Influence ofEthanol Blends on Low Speed Pre-Ignition in Turbocharged,Direct-Injection Gasoline Engines; SAE Paper 2019-01-0256 entitled‘Analysis of the Impact of Production Lubricant Composition and FuelDilution on Stochastic Pre-Ignition in Turbocharged, Direct-InjectionGasoline Engines’; U.S. Pat. No. 9,869,262B2 and U.S. Ser. No.10/208,691B2). The pressure levels are implicit to the LSPI detectionalgorithm and they need to be outside the normal combustion pressureconditions.

The variable used for LSPI detection in the present method is crankangle location at the start of combustion (method no. (3) above).

In summary, the step-by-step approach to detecting LSPI was:

Calculation of the average combustion cycle without pre-ignition todetermine pressure trace and SOC.

Definition of cycle SOC: +/−2% pressure above average (represented byPmax in the Figure) before a spark sets the trigger taking into accountthe burn delay.

Calculation of LSPI and knock characteristics based on the input fromthe above two factors, and continuously saving the pressure traces.

Multi-engine dynamometer was used for these experiments. Thesteady-state, i.e. constant speed and constant load, test procedure inFIG. 1a was used for engine tests herein unless another test procedureis explicitly mentioned. Steady-state tests consisted of operating theengine for 160,000 cycles for a total duration of 4 hours and 30 minuteswith a 2 minutes interval of coasting at the same speed but a lower loadto let the engine cool down to ambient conditions after each of the 4000engine cycles. Ten repeats of the cycle shown in FIG. 1 make up oneengine test. The LSPI events were counted initially for 160,000 cyclesand then scaled to a million cycles to finally report LSPI events inparts per million (ppm) unit (or events per million (epm)).

Transient state tests were incorporated into the test procedure toreflect real-life driving conditions.

A load-step method was incorporated into the long steady-state testprocedure whenever applicable. FIG. 1b and FIG. 1c display the load-stepmethod which acted as a quick ‘screener’ for the response of variouslubricant and calibration changes at very high loads (usually more than21 bar BMEP). The test procedure involved operating the steady-stateLSPI test at each load point for half the number of engine cycles (i.e.80,000 cycles) and then moving onto a higher load. Such a process helpeddetermine impact from changes in engine conditions or operating fluid toLSPI response in a relatively shorter amount of time without putting theengine through stress at very high loads where LSPI events can result inhigh and potentially damaging in-cylinder pressure values (P_(max)) Theload-step procedure was used when the objective was to explore themaximum BMEP achievable under certain engine conditions with a minimumamount of LSPI events. Few tests were also performed under transientconditions in order to understand the responsiveness of the engine torapid fluctuations in speed-load operating strategies (i.e. close toreal-life driving conditions). As shown in FIG. 1d , these conditionsinvolved a rapid increase in load for few seconds followed by coasting.These cycles were repeated for about 5-10 seconds for a total of 50,000cycles.

An important aspect of the test method is also the oil flushingprocedure consisting of four oil changes and filter changes interruptedby 30 minutes of engine operation to circulate the flushing oil.

LSPI Measurement Procedure

LSPI events are in general followed by large ‘aftershock’ (or following)events which could be both pre-ignition events induced by hot spots orknock events. However, these aftershock events cannot generally beconsidered as distinct LSPI events since they originate due to pressurewave reflections in the cylinder caused by the initial pre-ignitionevent. To differentiate between these events from the LSPI cycles,aftershock events are defined as pre-ignition events within three cyclesafter the leading pre-ignition event. If the following phenomenon occurswithin three cycles, the window for the second following event is againthree cycles after the first following event, etc. Independent eventsneed therefore to be minimum four cycles apart. Table 3 gives an exampleof how each LSPI events are reported in the present experiments.

TABLE 3 Example of LSPI Counts in 17 Combustion Cycles Pressure spike &SOC before spark LSPI or Cycle (1 = yes/2 = no) Aftershock? 1 2 None 2 2None 3 2 None 4 1 LSPI 5 2 None 6 2 None 7 1 Aftershock 8 2 None 9 1Aftershock 10 1 Aftershock 11 2 None 12 2 None 13 2 None 14 1 LSPI 15 2None 16 1 Aftershock 17 2 None No or LSPI, Aftershock and Total no ofevents: LSPI = 2; Aftershock = 4; Total events = 6 in 17 cycles

The engine specification used in the present examples is set out inTable 4 below:

TABLE 4 Displacement (cc) 1995  Compression Ratio 10:1 Bore (mm) 84Stroke (mm) 90 Max. Power (kW/hp) 200/270 Max. Torque (Nm/lb · ft)400/295 Aspiration Turbocharged (twin scroll) + cooled EGR FuelInjection Central DI Engine Name 2.0L GME-T4 (Global Medium EngineTurbocharged 4 Cylinder)

The test conditions sensitive to PM/PN formation and LSPI for thisengine are shown in Table 5 below. A AVL Microsoot sensor was used forrecording PM/PN.

TABLE 5 Coolant/Oil Operating Temperature Condition Test Type RPMLoad/BMEP [° C.] 1 Steady State 1500 10 bar 100 2 Steady State 2000  7bar 100 3 Steady State 2000 14 bar 100 4 Transient 2000 1 to 10 bar 30load step (VIT sweep; 310 to 240) 5 CAT Heating 1400 1.5 bar  30 6 DriveOff 1670 90 kPa MAP, 100 SA = 10, ATDC (approx.. 6.5 bar) 7 Coking 200010 bar 80 (2-3 hours) 8 LSPI Test Point 1500 21 bar 80

Table 6 below shows the Particulate Number (PN), number of LSPI eventsand the PM Index (as determined according to SAE Paper SAE-2010-01-2115)for each of the Fuels A-C. FIG. 2 is a plot of the results in Table 6.

TABLE 6 Fuel A B C PN (#/cm³) − 0.086 × 10⁷ 1.8 × 10⁷ 1.8 × 10⁷ CyclesAverage PN (#/cm³)  0.08 × 10⁷ 3.0 × 10⁷ 9.0 × 10⁷ Average − @LSPI PN(#/cm³) −  4.9 × 10⁷ 7.5 × 10⁷ 7.7 × 10⁷ @ Operating Condition 5 (1.5Bar, 1400 rpm) for Cat heating LSPI (ppm 0.00 2.31 14.56 Events, # × 10²PM Index 0.49 1.36 2.83

Table 7 below sets out the number of LSPI events per test for Fuels A, Band C, as well as the PM (as defined in SAE-2010-01-2115) and the PMIndex for each of Fuels A-C. FIG. 3 is a plot of the results shown inTable 7.

TABLE 7 Fuel A B C PM (mg/cm³) − 1.8 7.7 50 Cycles Average PM peaks 1.875 75 (mg/cm³) − @LSPI PN (mg/cm³) 1 15 45 Average − @ LSPI LSPI (ppm0.00 23.1 145.6 Events, ×10¹ PM (mg/cm³) − 5.20 14.70 19.80 @OperatingCondition 5 PM Index 0.49 1.36 2.83

DISCUSSION

The results in Tables 6 and 7 and in FIGS. 2 and 3 show that the fuelhaving the highest PM Index (Fuel C) also has the highest number of LSPIevents. Further, the fuel having the lowest PM Index (Fuel A) has thelowest number of LSPI events. Fuel C, which has a PM Index of 2.83,exhibits significantly higher level of LSPI events compared with Fuel Band Fuel A which have a PM Index of 1.36 and 0.49, respectively.

We claim:
 1. (canceled)
 2. (canceled)
 3. (canceled)
 4. (canceled) 5.(canceled)
 6. (canceled)
 7. (canceled)
 8. (canceled)
 9. (canceled) 10.(canceled)
 11. A method for reducing the occurrence of Low SpeedPre-Ignition in a spark ignition internal combustion engine, the methodcomprising supplying to the engine a gasoline fuel compositioncomprising a gasoline base fuel and having a PM Index of 1.4 or less.12. The method according to claim 11, wherein the spark-ignitioninternal combustion engine is a direct injection spark-ignition internalcombustion engine.
 13. The method according to claim 12, wherein thegasoline fuel composition has a PM Index of 1.0 or less.
 14. The methodaccording to claim 12, wherein the gasoline fuel composition has a PMIndex of 0.8 or less.
 15. The method according to claim 12, wherein thespark-ignition internal combustion engine is lubricated with a lubricantcomposition comprising 500 ppmw of calcium or greater, based on thetotal lubricant composition.
 16. The method according to claim 15,wherein the lubricant composition comprises from 1000 ppmw of calcium orgreater, based on the total lubricant composition.
 17. The methodaccording to claim 15, wherein the lubricant composition comprises 1500ppmw of calcium or greater, based on the total lubricant composition.18. The method according to claim 15, wherein the lubricant compositioncomprises 1000 ppm or magnesium or less, based on the total lubricantcomposition.
 19. The method according to claim 15, wherein the lubricantcomposition comprises a zinc-based anti-wear additive in an amount of1200 ppmw or less, based on the total lubricant composition.
 20. Themethod according to claim 15, wherein the lubricant compositioncomprises a molybdenum-based friction reducing agent at a level of 1000ppmw or less, based on the total lubricant composition.